Ancient DNA Explains How Chickens Got To The Americas

On Thanksgiving, as many as 88% of American households put turkey, a bird native to North America that was first domesticated by the Mayans, on their table. But a small fraction of us choose to serve something else -- most often, chicken. Although the chicken is incredibly popular in the U.S., with Americans eating close to 100 lbs per person per year, the origins of the bird and its importation to the New World are somewhat murky.

The chickens that we eat today appear to have all descended from the red junglefowl (Gallus gallus). Prior to the advent of fast, inexpensive DNA analysis, the origins of chickens were traced using archaeology, history, linguistics, and the morphology or physical appearance of the birds. But a 2012 article published in PLoS One by Australian anthropologist Alice Storey and her colleagues used mitochondrial DNA to figure out where chickens came from and how they made their way around the world.

A Ceylon junglefowl (Gallus lafayetii) is pictured at the Yala National Park. (Ishara S.KODIKARA/AFP/Getty Images)

Unlike animals such as monkeys, which are known to have migrated from the Old to the New Worlds, chickens are not naturally migratory. They have a small home range and can't fly or swim well. Their distribution throughout the world, then, is directly related to humans' interest in the creatures.

Chickens were likely first domesticated about 5,400 years ago in Southeast Asia, although archaeological evidence ofwild chickens goes back even further, to a 12,000-year-old site in northern China. Once domesticated, though, chickens were brought westward to Europe and east-southeast into Oceania. One of the main chicken-related research questions, however, remains: how did they get to the Americas?

According to Storey and colleagues, the domestic chicken came to the Americas by multiple routes. One of those routes was from Europe, when Dutch and Portuguese slave traders brought chickens over from Africa in the 16th century. The researchers' DNA investigation of archaeological chicken bones from eastern New World sites in Haiti and Florida, for example, suggests that the introduction of chickens in this area of North America came in the 1500s and 1600s, and that these animals share genetic similarities with chickens from archaeological sites in Spain dating to the same period.

However, the oldest route for importation of chickens to the Americas appears to be through Polynesia prior to Columbus. At the archaeological site of El Arenal in coastal Chile, excavators found 50 chicken bones that represented at least five different chickens. As Storey and colleagues report in another article in the Proceedings of the National Academy of Sciences, the site has been confidently dated to 700-1390 AD, meaning these bones are the earliest evidence of chickens in the Americas, having arrived at least a century before Columbus. Radiocarbon dates, isotope information, and mitochondrial DNA all agree with the archaeological evidence of a pre-Columbian introduction of domesticated chicken to South America.

The question of the date of importation of chickens to the New World, though, is not completely settled. According to Storey and colleagues, "perhaps the most striking result reported" in their PLoS study "is the evidence that the haplogroup E chickens were taken in opposite directions out of Asia, and their histories and dispersal pathways finally converged in the Americas after A.D. 1500." That is, from southern Asia, chickens were brought east and west, eventually ending up in the same place in the Americas around the same time.

Two major problems affect our current understanding of the origin and spread of chickens, however. First, as Storey and colleagues note, the low genetic diversity in chickens means difficulty tracing their genetics, and additional studies of variability across the chicken genome are needed. Second, chickens are difficult to find archaeologically. Zooarchaeologist Tanya Peres of Florida State University explains that "chicken bones are thin, prone to breakage, and don't survive as whole elements." This means that many archaeological specimens that might be chicken are currently categorized as generic birds. "Added to the fragmentary nature of the bones," Peres notes, "are eggshells. They're not easy to identify to a genus or species. It may be that chickens were especially important as egg layers versus as a meat resource."

Skillet glazed spicy sweet potatoes. (AP Photo/Matthew Mead)

Although we don't know which was eaten first -- the chicken or the egg -- tracing the origins of chickens actually gives us insight into another Thanksgiving staple. That is, the Pacific chicken route was not one-way. There is additional evidence that sweet potatoes - a native food of the Americas - made their way west into Oceania around the same time as chickens were moving east. Contact between Polynesian peoples and natives of South America appears to have been purposeful and long-lasting.

So this Thanksgiving as you chow down on roast chicken and sweet potato pie, be sure to thank the intrepid Pacific explorers who, thousands of years ago, braved the ocean to bring birds and tubers to your dinner table!

As a bioarchaeologist, I routinely pore over the skeletons of ancient populations so that I can learn about their health, diet, and lifestyles. (PhD anthropology, MA classical archaeology)